Benefication of potash

ABSTRACT

Potash is subjected to a rougher gravity beneficiation to remove significant amounts of halite and the overflow is subjected to a cleaner gravity beneficiation to provide an overflow concentrate. The underflow from the cleaner gravity separation is sized to provide finer particles which can be beneficiated to provide a product having a high K2O content.

United States Patent Dancy July 17, 1973 [54] BENEFICIATION OF POTASH 3,337,328 8/1967 Lawver 241/24 X [75] Inventor: William B. Dancy, Lakeland, Fla. FOREIGN PATENTS 0R APPLICATIONS [7 3] Assignee: International Minerals & Chemical 1 g -yrea n in... Corponmn Lbmyvme 792,819 8 1968 Canada 209 172.5 [22] Filed: Oct. 2, 1970 No-Z Primary Examiner-Frank W. Lutter Assistant Examiner-Robert I-Ialper Attorney-James E. Wolber and Peter Andress [52] US. Cl 241/20, 209/17, 209/166, 209/ 172.5 [51] Int. Cl B03b 7/00 [57] ABSTRACT [58] Field of Search 209/17, 12, 172473, Pmash sublected mughe' Emmy benefimm" 209/211. 241 20 24. 23/ 9 38 2 to remove significant amounts Of halite and the CV61- flow is subjected to a cleaner gravity beneficiation to [56] References Cited provide an overflow concentrate. The underflow from UNITED STATES PATENTS the cleaner gravity separation is sized to provide finer particles which can be beneficiated to provide a prod- 2,726,763 12/1955 Rakowsky 209 211 x uct having a high K 0 content 2,846,068 8 1958 Smith 209/166 2 3,167,502 l/l965 Duke 209/12 11 Claims, 1 Drawing Figure GTE CRUSHER 3 4 IOM f s l7 HYDROCYCLONE l3 M TAILS PRODUCT HYDROCYCLONE T Patented July 17, 1973 CRUSHER ORE H YDROCYC LONE TAILS PRODUCT HYDROCY'CLONE I I5 CRUSHER I I8 DESLIME PRODUCT FLOTAT-l ON BENEFICIATION OF POTASH DESCRIPTION OF THE INVENTION This invention relates to the beneficiation of potash ores and more particularly to the beneficiation of potash ores by gravity separation.

Potash ore such as sylvinite is primarily a mixture of sylvite (KCl) and halite (NaCl) although other salts may be present in minor proportions. In order to provide a commercial product it is necessary to beneficiate the ore to provide concentrates that may have a K content of 50 percent or 60 percent or more. Since potash is a relatively low-priced bulk commodity, beneficiation efficiency is particularly important.

It is one object of this invention to provide a process for the beneficiation of potash ore.

It is a further object of this invention to provide a process for the beneficiation of potash ore by gravity separation.

It is an additional object of this invention to provide a process wherein a rougher gravity separation and a cleaner gravity separation is employed for the beneficiation of potash.

It is another object of this invention to provide a process wherein the underflow from the cleaner gravity separation is sized to provide finer particles which may be beneficiated to provide a fraction characterized by a high potash content.

The present invention contemplates a process for beneficiating a potash ore containing sylvite and halite comprising:

1. comminuting the ore to substantially liberate the mineral constituents;

2. sizing said comminuted ore to remove the finer particles and provide a larger size fraction composed principally of coarser particles;

3. subjecting said larger size fraction to gravity separation in a media having a specific gravity of separation intermediate the specific gravity of sylvite and halite whereby sylvite-containing particles are removed as an overflow fraction and halite particles are removed as an underflow fraction;

4. subjecting the overflow from said gravity separation of (3) to a gravity separation in a media having a specific gravity of separation intermediate the specific gravity of sylvite and halite whereby a sylvite concentrate is obtained as an overflow and an underflow is obtained;

5. sizing said underflow from said gravity separation of (4) to provide finer particles including a substantial number of particles having a high K,O content; and

(6) recycling said finer particles from to the gravity separation of (3). In one preferred embodiment, the coarser fraction from the cleaner underflow is comminuted and returned to the rougher separation. In another preferred embodiment of the invention, the finer particles from the sizing of (2) are subjected to wet beneficiation, i.e. froth flotation or crystallization.

The underflow from a potash cleaner gravity separation is generally regarded as middlings made up of particles of locked" sylvite and halite. In conventional processing the underflow or cleaner middlings stream is comminuted to break down the locked particles and the comminuted material essentially reports to flotation or crystallization processes as -l0 mesh material. This invention is premised on the discovery that the underflow from the cleaner separation contains smaller particles including a substantial number of liberated sylvite particles. A sizing of the underflow permits recycle of these particles directly to the gravity separation.

Separation of small size particles and direct recycle minimizes the load on the middlings crusher and recycle circuit and avoids unnecessary generation of very fine particles which require wet beneficiation. The process of this invention increases the production of larger particles which, because of their size, constitute premium product.

The beneficiation of sylvinite by gravity separation is described in detail in Canadian Pat. No. 792,819 and the process of this invention constitutes an improvement within the ambit of Canadian Pat. No. 792,819.

It is particularly designed for the beneficiation of potash ore containing sylvite and halite such as sylvinite found in Saskatchewan. Such ores generally will contain from about 25 to about 30 percent sylvite. In addition to sylvite and halite, the ore may also contain minor amounts of constituents such as polyhalite, kainite, keiserite, magnesium sulfate and/or leonite. Generally comminution to about three-eighths inch provides liberation of mineral constituents. The term liberation is employed herein to designate that degree of comminution which permits the ore to be physically separated into a concentrate having an analysis of 55 percent K,O or more. It will be appreciated that liberation of mineral constituents of specific ore deposits may vary somewhat from three-eighths inch.

For ease of presentation, the practice of the invention will be described hereinafter with reference to the processing of a inch X+l0 mesh ore fraction. The mesh sizes referred to herein are standard Tyler mesh sizes.

The process of this invention readily can be carried out employing standard equipment well known in the art. For example, either wet or dry comminution may be employed in the practice of this invention, and suitable apparatus includes a ball mill, hammer mill, rod mill, impact crusher, or the like. Such equipment will provide particles ranging from a selected maximum size downward.

Comminution will, of course, provide some fines which may interfere with the gravity separation by altering the specific gravity of the medium or by interfering with the separation of weighting agent from the ore particles. Accordingly, the comminuted ore is sized employing hydrocones, rake classifiers, screens, or the like to remove at least about the -10 mesh fraction. The l0 mesh fraction may be deslimed and beneficiated by conventional flotation or crystallization techniques as will be discussed more fully below.

The sized ore (about inch X about +10 mesh) is subjected to gravity separation employing a liquid that has a gravity intermediate the gravity of halite (approximately 2.17 at 20 C) and sylvite (approximately 1.99 at 20 C). Typical vessels employed for gravity separation include cones, classifiers, drum-type vessels or vortex separatory vessels such as hydrocyclones.

The liquid media employed for the gravity separation may be either a so-called heavy media or a so-called heavy liquid. A heavy media is a suspension. of a weighting agent, or a mixture of weighting agents, in a brine which is preferably substantially saturated with respect to the sylvinite feed. Ferrous media, such as magnetite and/or ferrosilicon, are preferred weighting agents because of their commercial availability, low cost, ease of recovery and cleaning by magnetic means, and ability to form a fluid medium of the predetermined specific gravity in the brine. The ferrous media are usually used as'substantially all minus 100 mesh particles. These are very readily suspended in the brine and the resultant suspension is self-sustaining with the moderate agitation produced by recycling the suspension in the normal operation. l-lalogenated hydrocarbons and mixtures thereof are suitable for use as heavy liquids. lllustrative of such halogenated hydrocarbons are methylene bromide (specific gravity of 2.49) and methylene chlorobromide (specific gravity of 1.92). Fluorine substituted and iodine substituted alkyl compounds may also be used.

The terms circulating gravity and specific gravity of separation will be used herein in accordance with the general usage in the art. Thus, circulating gravity means and refers to the actual density of the separating medium, while specific gravity of separation means and refers to the apparent density of the separating medium based on the separations which can be made with it in a specific separating vessel. When the separatory vessel used is one in which the path taken by the individual particles is determined only by their respective specific gravities, such as a conventional cone, classifier or drum-type vessel, the circulating gravity and specific gravity of separation will be the same. In such instances, the separating medium (either circulating or in the separation vessel) will have a specific gravity intermediate the specific gravities of the sylvite and halite. However, when a vortex separatory vessel is employed as in the preferred embodiment of this invention, use is made of centrifugal forces which are many times greater than gravity. In such instances, a given heavy media may itself have a specific gravity, i.e. a circulating gravity, of less than the gravity of either halite or sylvite but may produce a separation in a vortex vessel such as a hydrocyclone between the sylvite and the halite because the forces in the vessel provide a heavier specific gravity of separation. For example, a circulating gravity of 1.85 may provide a media in the vortex vessel that has the characteristics of a 2.1 specific gravity. Thespecific gravity of separation of such a heavy media would then be said to be about 2.1. The relationship between circulating gravity and specific gravity of separation will vary somewhat depending upon the apparatus and operating conditions but is readily within the skill of the routineer. I

Gravity separation provides a sylvite-containing overflow and an underflow that is relatively poorer in sylvite values. In the process to which this invention is directed, the ore is subjected to both a rougher and to a "cleaner separation. The specific gravity of separation for the rougher" separation generally will be between about 2.10 and about 2.16 while the specific gravity of separation for the cleaner separation will be between about 2.02 and about 2.06. When employing both a rougher and cleaner separation, the overflow sylvite-containing fraction from the rougher is sent to the cleaner and the overflow from the cleaner constitutes the sylvite concentrate. l-lalite tails are rejected as underflow from the rougher. The underflow from the cleaner is processed accordingto this invention by removing the finer particles therefrom and recycling those particles to the rougher gravity separation, either directly or through a l mesh sizing operation. The

coarser particles from the cleaner underflow may be comminuted and recycled to the rougher separator. Generally particles having a size of less than about 4 mesh are the particles suitable for direct recycle and the larger particles in the cleaner underflow appropriately can be comminuted to about -4 mesh for recycle since it has been determined that comminution to only about 4 mesh is adequate to liberate completely the values of these particles. While 4 mesh is often a satisfactory size to separate finer liberated particles from coarser locked particles, it will be understood that for particular ores or processes separation may occur at other sizes such as 6 mesh or the like. The appropriate size for any particular circumstance readily can be determined by one skilled in the art. Comminution can be expected to generate some -10 mesh material which desirably is removed from the gravity separation circult.-

It is likely that sufficient -l0 mesh material will be generated in the process to justify beneficiation of this material also. This material can be beneficiated readily by either conventional froth flotation or by conventional crystallization. The term wet "beneficiation" is employed herein to denote either froth flotation or crystallization.

In a conventional wet beneficiation of l0 mesh particles, slirnes can be removed in a hydro-separator and the deslimed ore beneficiated. ln froth flotation, the ore may be reagentized with a cationic flotation agent, and the fraction subjected to froth flotation. Suitable cationic flotation agents include aliphatic amines, such as n-lauryl amine, and high molecular weight aliphatic amines containing about 14 to 20 carbon atoms and their water-soluble addition salts, as well as quaternary ammonium salts, as for example, octadecylamine acetate, hexadecylamine hydrochloride, and the like. The conditioned ore is finally fed into a suitable flotation vessel, which usually consists of a battery of units in parallel or in series. The flotation is effective to remove as an overflow concentrate a substantial amount of the sylvite content of the fine fraction together with some of the halite. The flotation concentrate is dried and sent to storage. The underflow tail from the flotation operation, predominating in halite and containing a minor amount of sylvite, is removed and discarded as waste.

In a conventional crystallization process, ore is contacted with heated brine unsaturated with respect to KCl but saturated with respect to NaCl in order to solubilize KCl in the ore. Thereafter, the brine is cooled to deposit KCl crystals. Since thesolubility of NaCl is not affected by temperature changes in the same manner as NaCl, the process tends to be selective for the production of KCl crystals.

The accompanying drawing is a diagrammatic flow sheet illustrating a preferred embodiment of the process of this invention.

Ore is fed to crusher 1 to provide inch particles. Oversize is removed by screen 2 and recycled through line 3 to crusher l. The fraction is then sized at screen 4 to remove 10 mesh material and provide a fraction containing particles ranging from about inch to about 10 mesh. The 56 inch X 10 mesh fraction is removed from screen 4 through line 5 to rougher gravity separator hydrocyclone 6 desirably having a specific gravity of separation of about 2.10 to about 2.16. An underflow containing halite is rejected as tails through line 7 while an overflow containing sylvite values is removed through line 8 and is sent to cleaner hydrocyclone 9, desirably having a specific gravity of separation of from about 2.02 to about 2.06. An overflow sylvite product is removed from hydrocyclone 9 through line 10. Underflow middlings, removed from hydrocyclone 9 through line 11, are screened at screen 12 to provide -4 mesh particles which are recycled through line 13 to rougher hydrocyclone 6. Alternatively, the particles can be recycled to screen 4 for the removal of any mesh material present. The +4 mesh particles from screen 12 are removed through line 14 and comminuted to about 4 mesh in crusher 15. The comminuted particles are then recycled through line 16 to screen 4 so that 10 mesh particles can be removed from the circuit. If desired, the -10 mesh particles can be removed from the crusher output and that stream can then be recycled to rougher hydrocyclone without first passing through screen 4.

The l 0 mesh fraction from screen 4 is sent through line 17 to hydro-separator 18 for desliming and subjected to cationic froth flotation in flotation circuit 19. Flotation yields a sylvite product which is removed through line 20 and an underflow halite tailings which is removed through line 21.

It should be noted that the ancillary equipment normally associated with a hydrocyclone is not shown in the attached figure. Thus, for example, if the initial comminution and sizing are dry, fractions will be sent to a pulper wherein the ore is pulped with brine to provide a slurry. Ifdesired, magnetite can also be added to the pulper to provide the requisite circulating specific gravity. It is also possible, however, to employ an initial pulping operation wherein the ore is pulped with brine and also to provide a second pulping operation in which magnetite and additional brine, if necessary, are added to provide the requisite circulating specific gravity. Similarly, weighting agents or heavy liquids are commonly removed from the hydrocyclone overflow and underflow streams by screening, brine washing or the like. It is possible to process intermediate stream 8 containing heavy media or heavy liquids without intermediate removal of the heavy media or liquid. in such event, however, care must be taken not to upset the desired gravity in the cleaner gravity separation due to uncontrolled carry over of heavy media or liquid from an earlier gravity separation.

The following example is included for illustrative purposes only and is not intended to limit the scope of the invention.

EXAMPLE 1 Fifteen thousand parts of mine run sylvinite ore from the Williston basin region of Saskatchewan containing 3,970 parts of K 0 is comminuted to inch and is sized to remove 10 mesh particles. The inch X 10 mesh fraction, 10,890 parts containing 2,660 parts K 0, is subjected to a rougher gravity separation in a hydrocyclone at a specific gravity of separation of about 2.12.

The rougher separation provides 5,930 parts of overflow concentrate containing 2,530 parts K 0. Underflow tails total 4,960 and contain 130 parts K 0.

The rougher overflow is subjected to a cleaner gravity separation in a'hydrocyclone at a specific gravity of separation of about 2.04. The cleaner separator provides 3,200 parts of overflow sylvite product containing 1,930 parts K 0.

The underflow from the cleaner separator consists of 2,730 parts containing 600 parts of K 0. This stream is sized at 4 mesh and the 4 mesh fraction is recycled to the initial 10 mesh screening operation and then to the rougher separator while the +4 mesh fraction is comminuted to 4 mesh and recycled to the initial 1 0 mesh screening operation.

The -10 mesh material from the initial screen operation totals 6,840 parts containing 1,910 parts K 0. This material is subjected to froth flotation and provides 2,870 parts concentrate containing 1,750 parts K 0. A tailing consisting of 2,870 parts and containing 160 parts K 0.

In order to demonstrate the advantages achieved by the process of this invention, the above process is duplicated on another 15,000 parts of the same sylvinite ore except that the entire underflow from the cleaner separator is comminuted through a crusher set at 10 mesh. The comparative results are shown in Table 1.

TABLE 1 Ex 1 Control (weight parts) (weight parts) Gravity Concentrate Total 3,200 2,870 K 0 1,930 1,750 10 Mesh to Flotation Total 6,840 7,850 K 0 1,910 2,130 Flotation Concentrate Total 2,870 3,210 K 0 1,750 1,950 Product Total 6,070 6,080 K 0 3,680 3,700 Coarse 8L Granular Total 2,710 2,580 K 0 1,640 1,570 Standard 14M X Total 3,360 3,500 K 0 2,040 2,130

The data of Table 1 demonstrate that less 10 mesh material is generated by the process of this invention and correspondingly less material therefore need be beneficiated by froth flotation.- While the total recovery is about the same in each case, this invention provides more product from the gravity separation and, importantly, moretotal premium product (coarse & granular). 1n the control, 42 percent of the total K 0 was premium whereas 58 percent was in the less desirable finer or standard size. This invention provided 45 percent of the K 0 as premium and 55 percent as standard.

EXAMPLE 2 An underflow from a cleaner separation was divided into several size fractions. Each fraction was analyzed for K 0 content and was subjected to gravity separation at a specific gravity of separation of 2.05. The results are shown in Table 2.

TABLE 2 Gravity Separation Underflow Concenuate Tails %K,O

+51!" 2.1 17.4 52.9 12.9 33.9 %"X%" 12.1 15.4 57.2 10.2 40.9 16"X4M 11.0 22.8 58.8 9.5 69.7 4MX6M 18.2 23.9 60.2 5.6 84.5 6MX8M 18.1 23.8 61.2 4.6 87.4 8MX10M 18.2 20.7 61.6 3.8 87.0 l0M 20.3 19.2 61.7 3.8 85.4

The data of Table 2 demonstrate that about 75 percent of the underflow was 4 mesh and that gravity separation of this material did produce at least 60 percent K concentrate in good yield without further comminution. This data demonstrate, therefore, that the throughput of the underflow crusher can be reduced significantly compared to that required in the control process.

EXAMPLE 3 The +4 mesh fraction from the cleaner gravity separation underflow was crushed in a jaw crusher to 4 mesh and subjected to gravity separation at a specific gravity of separation of about 2.05. The results are shown in-Table 3.

TABLE 3 Parts K 0 Wt. %K,O K 0 Distribution Feed 100 19.77 V 19.77 100 Overflow Concentrate 26.6 60.8 16.17 8 I .8 Underflow Tails 73.4 4.9 3.6 18.2

The data of Table 3 demonstrate that comminution to 4 mesh is appropriate to provide particles susceptible of substantial sylvite recovery.

The K 0 content noted above, and employed throughout this specification, refers to the potassium values present in the ore as sylvite.

Since variations of the invention will be apparent to those skilled in the art, it is intended that this invention be limited only by the scope of the appended claims.

I claim:

are removed as an underflow fraction;

4. subjecting the overflow from said gravity separation of (3) to a gravity separation in a liquid media having a specific gravity of separation intermediate the specific gravity of sylvite and halite whereby a sylvite concentrate is obtained as an overflow and an underflow is obtained;

5. sizing said underflow from said gravity separation of (4) at about 4 mesh to separately provide larger particles and finer particles including a substantial number of particles having a high K 0 content; and

6. recycling said finer particles from (5) to the gravity separation of (3).

2. A process according to claim 16 wherein said gravity separations are vortex gravity separations.

3. A process according to claim 2 wherein a magnetite-containing heavy media is employed in the gravity separations 4. A process according to claim 1 wherein the l0 mesh particles from the process are subjected to wet beneficiation.

5. A process according to claim 4 wherein the wet beneficiation is froth flotation.

6. A process according to claim 1 wherein the wet beneficiation is crystallization.

7. A process according to claim 1 wherein the spe cific gravity of separation of (3) is from about 2.10 to about 2.16 and the specific gravity of separation of (4) is from about 2.02 to about 2.06.

8. A process according to claim 7 wherein said gravity separations are vortex separations.

9. A process according to claim I wherein the larger particles from (5) are comminuted to about 4 mesh and are recycled to the gravity separation of (3).

10. A process according to claim 1 wherein said larger particles of step (5) are comminuted and recycled to the gravity separation of step (3).

11. A process according to claim 1 wherein said gravity separation of (3) is a vortex gravity separation at a specific gravity of separation of from about 2.10 to about 2.16; said gravity separation of (4) is a vortex gravity separation at a specific gravity of separation of from about 2.02 to about 2.06; and the larger particles of step (5) are comminuted and recycled to the sizing of (2).

UNITED STATES PATENT OFFICE CEHFICATE 0F CORRECTION Patent No. 3 1 746 265 Dated July 17 1973 lnventofls) William B. Dancy It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 8, claim 2, line 1, delete "16 and substitute l-.

' Signed and Scaled this fif Day Of August1975 [SEAL] Atfesl.

RUTH C. MASON C. MARSHALL DANN IIHSII HX ()jfiter ('mnmisxinm'r uj'lulrnts and Trudcmurkx 

2. A process according to claim 16 wherein said gravity separations are vortex gravity separations.
 2. sizing said comminuted ore to provide a fraction substantially free of particles smaller than about 10 mesh;
 3. subjecting said fraction to gravity separation in a liquid media having a specific gravity of separation intermediate the specific gravity of sylvite and halite whereby sylvite-containing particles are removed as an overflow fraction and halite particles are removed as an underflow fraction;
 3. A process according to claim 2 wherein a magnetite-containing heavy media is employed in the gravity separations.
 4. A process according to claim 1 wherein the -10 mesh particles from the process are subjected to wet beneficiation.
 4. subjecting the overflow from said gravity separation of (3) to a gravity separation in a liquid media having a specific gravity of separation intermediate the specific gravity of sylvite and halite whereby a sylvite concentrate is obtained as an overflow and an underflow is obtained;
 5. sizing said underflow from said gravity separation of (4) at about 4 mesh to separately provide larger particles and finer particles including a substantial number of particles having a high K2O content; and
 5. A process according to claim 4 wherein the wet beneficiation is froth flotation.
 6. A process according to claim 1 wherein the wet beneficiation is crystallization.
 6. recycling said finer particles from (5) to the gravity separation of (3).
 7. A process according to claim 1 wherein the specific gravity of separation of (3) is from about 2.10 to about 2.16 and the specific gravity of separation of (4) is from about 2.02 to about 2.06.
 8. A process according to claim 7 wherein said gravity separations are vortex separations.
 9. A process according to claim 1 wherein the larger particles from (5) are comminuted to about -4 mesh and are recycled to the gravity separation of (3).
 10. A process according to claim 1 wherein said larger particles of step (5) are comminuted and recycled to the gravity separation of step (3).
 11. A process according to claim 1 wherein said gravity separation of (3) is a vortex gravity separation at a specific gravity of separation of from about 2.10 to about 2.16; said gravity separation of (4) is a vortex gravity separation at a specific gravity of separation of from about 2.02 to about 2.06; and the larger particles of step (5) are comminuted and recycled to the sizing of (2). 